The invention relates to novel processes and devices for the analysis of samples of very small volume, which will be referred to hereafter under the general term "micro-analyses".
The practice of analysing very small quantities of a substance is dictated by different considerations. Among these can be mentioned the very high cost of certain reagents and the fact that certain reagents are only available in limited quantities, but the principal reason is in only having very small samples available. These constraints are frequent in the field of biochemical analyses and more particlarly in certain medical diagnosis analyses. A particular field of use of micro-analysis techniques is that of enzymatic analysis.
A decisive advantage of the use of very small volumes is the improvement in signal/background noise ratio in the measurement of the observed phenomena. Thus, when an enzymatic reaction is carried out in which the enzymatic activity is very low, the presence of a disporportionate amount of substrate can compromise the measurement. In fact, the substrates used for this type of analysis are never perfectly pure, and the background noise, due to these impurities, makes the signal difficult to read. It is thus desirable, for reactions of this type, to reduce the volume of substrate to quantities comparable with those of the substances to be analysed. Consequently, the background noise is reduced without the signal being modified, which makes the measurement easier and more reliable.
The use of very small amounts of substance in the implementation of the reactions raises particular difficulties connected with the handling of the samples and of the reagents used during these analyses. It is to these that the invention relates.
For the exact measurement of liquid samples of small volume, the instruments principally used at the present time are of the constriction pipette type or microsyringe type. These instruments are however not very convenient in use, even impossible to use when the volumes treated become too small, in particular when the sample or the reagent of measured volume must be constituted as it is, i.e. without being volatilized (as in gas chromatography) or without being introduced into a liquid medium of much larger volume. Thus, under the effect of the electrostatic forces, the droplets of small volume, when they are separated from the instrument which serves to form them, have a tendency to burst spontaneously. The mixture of two droplets, for reacting them, is also a problem, since the forces of cohesion of each of them are opposed to their fusion.
The invention has as its aim to provide a device and process which facilitate the use of reagents and samples in micro-analysis techniques and to improve the accuracy and sensitivity thereof. In particular, the object of the invention is to provide a very accurate measurement of the reacted constituents and to ensure the proper formation of the mixture thereof, so that the reaction can develop normally.